The polyphenylene ethers and processes for their preparation are known. Various processes for their preparation are described in numerous publications including Hay, U.S. Pat. No. 3,306,874 and 3,306,875. Other procedures are described in Van Dort, U.S. Pat. No. 3,365,422, Bennett and Cooper, U.S. Pat. Nos. 3,639,656; 3,642,699; 3,733,299; 3,838,102 and 3,661,848. All of these patents are incorporated herein by reference.
The processes most generally employed in the preparation of polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen containing gas and a catalyst. Thereafter, various procedures including the use of chelating agents, have been employed to extract the catalyst into an aqueous phase which can be separated from the polymer solution. If the chelate is soluble in the precipitating medium, the phases are not separated before the polymer is precipitated with an appropriate antisolvent.
Active catalyst systems have been developed for the preparation of 2,6-disubstituted phenolic compounds. These systems are disclosed in U.S. Pat. No. 3,914,266 which is hereby incorporated by reference. Those systems comprise a diamine, a copper compound, a tertiary amine, and a bromide source. It has been observed that these catalyst systems are extremely active and permit a reduction in the time required to obtain polyphenylene ether resins having commercially acceptable properties.
A practical disadvantage in the use of this type of catalyst is the extremely rapid rise in molecular weight which occurs during the build stage of polymerization. This rapid rate of polymerization makes it very difficult to control the molecular weight of the final product. Typically, the intrinsic viscosity may increase by 0.2 dl/g (as measured in CHCl.sub.3 at 30.degree. C) in a period of five minutes, so that an error of only a minute or so in terminating the reaction may result in an unacceptable product. This points up the desirability of a polymerization system which produces a more gradual increase in molecular weight, preferably self limiting systems in which polymer growth stops when the desired molecular weight is reached.
It has now been found that the build stage of polymerization using the above described diamine catalyst system, may be moderated by the inclusion of a small amount of water in the initial polymerization mixture. Only a small amount of water is required to achieve this result.
The profound effect of small amounts of water added at the start of the reaction is particularly surprising as the amounts of water that are required are substantially less than the amounts of water that are produced as a by-product of the polymerization reaction.
Accordingly, it is a primary object of the invention to provide a method for moderating the rate of diamine catalyzed polyphenylene ether polymerization to permit more precise control of the molecular weight of the polymer.
It is also an object of this invention to provide a method for moderating the rate of diamine catalyzed polyphenylene ether polymerization reactions with an agent that may be easily separated from the polymer product.